Part 1 The diastereoisomerically enriched N-phosphinoy1-0-sulphon-ylhydroxylamines PhCHMeP(O)(Ph)NHOX [X = methanesulphonyl (Ms) or p-nitrobenzenesulphonyl (Ns)] react with MeNH2 and ButNH2 (neat, 1.0 M, and 0.1 M in CH2C12) to give the expected diamide rearrangement products PhCHMeP(O)(NHPh)NHR (R = Me or But). The rearrangement proceeded with high stereospecificity for all concentrations of MeNH2 and for neat ButNH2. Single crystal X-ray analysis revealed that rearrangement with MeNH2 proceeded largely with retention of configuration at phos-phorus. Stereochemical and competition studies on PhCHMeP(O)(Ph)NHOX (X = Ms or Ns) and studies on the enant-iomers of Ph2P(O)NHOS(O)2Camphor have provided strong evidence for phosphonamidic-sulphonic mixed anhydride RP(O)(NHPh)OX (X = Ms or Ns) involvement in the rearrangement. MeNH2 and ButNH2 also reacted with PhCHMeP(O)(Ph)NHOMs (SN2 at N) giving the hydrazides PhCHMeP(O)(Ph)NHNHR (R = Me or But). This was more important for ButNH2 and competition studies with (Me-C6H4-CH2)2P(O)NHONs using equimolar mixtures of ButNH2-ButMeNH and ButNH2-Pri2NH showed that ButMeNH was 11.5 times better than ButNH2 for hydrazide formation while ButNH2 was only slightly better than Pri2NH. Part 2 The diastereoisomers of the a-bromomethylphosphonamidate BrCH2P(O)(NHBut)OMenthyl react with PhCH2N+Me3 -OMe (QOMe) to give the aminomethylphosphonate ButNHCH2P(O)(OMe)OMenthyl and phosphoramidate ButMeNP(O)(OMe)OMenthyl products resulting from the breakdown of an azaphosphiridine oxide intermediate. Single crystal X-ray analysis revealed that the aminomethyl-phosphonate was formed with inversion of configuration at phosphorus and that the phosphoramidate was formed very largely with retention of configuration at phosphorus, prov-iding further evidence for azaphosphiridine oxide involvement. The a-bromomethylphosphonamidates BrCH2P(O)(NHBut)OR (R = Me, Cyclohexyl, or But) react with QOMe and KOBut to give the corresponding aminomethylphosphonate and phosphoramidate rearrangement products. It was found that bulky OR groups in the substrate and bulky alkoxides enhance the yield of the aminomethylphosphonate product.